Light emitting diode with light emitting layer containing nitrogen and phosphorus

ABSTRACT

Embodiments of the invention include an n-type region, a p-type region, and a light emitting layer disposed between the n-type region and the p-type region. The light emitting layer is a III-V material comprising nitrogen and phosphorus. The device also includes a graded region disposed between the light emitting layer and one of the p-type region and the n-type region. The composition of materials in the graded region is graded.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/411,926 filed on Dec. 30, 2014, titled “LIGHT EMITTING DIODEWITH LIGHT EMITTING LAYER CONTAINING NITROGEN AND PHOSPHORUS”, which isa § 371 application of International Application No. PCT/IB2013/055161filed on Jun. 24, 2013, which claims priority to U.S. Provisional PatentApplication No. 61/668,053 filed on Jul. 5, 2012. U.S. patentapplication Ser. No. 14/411,926, International Application No.PCT/IB2013/055161, and U.S. Provisional Patent Application No.61/668,053 are incorporated herein.

FIELD OF THE INVENTION

The present invention relates to a light emitting device including aIII-V light emitting layer including both nitrogen and phosphorus.

BACKGROUND

Light emitting diodes (LEDs) are widely accepted as light sources inmany applications that require low power consumption, small size, andhigh reliability. Diodes that emit light in the yellow-green to redregions of the visible spectrum contain active layers formed of anAlGaInP alloy, often grown on a GaAs substrate. Since GaAs is absorbing,it is typically removed and replaced by a transparent substrate.

U.S. 2009/0108276 states “[t]here are a number of known difficultieswith currently used yellow-red AlInGaP-based light emitting devices. Forexample, they suffer from low internal quantum efficiency and poortemperature stability in the yellow-red range, which is usuallyattributed to poor electron confinement. In addition, the conventionalprocedure for removing the light absorbing GaAs substrate and waferbonding a transparent substrate or reflective layer to the formed layerhas a low yield and adds several relatively expensive processing steps,thus resulting in high costs.”

FIG. 1 illustrates an LED structure described in paragraph 21 of U.S.2009/0108276. In FIG. 1, “the LED structure may comprise a GaP substrate[10] over which is formed a GaP buffer layer [12], over which is formedan active region [14] comprising interleaved layers of a GaP barrierlayer and a InmGa1-mNcP1-c layer where 0.001<c<0.05 and 0≤m≤0.4 activelayer, over which is formed a GaP cap/contact layer [16]. In someembodiments of this specific structure, the GaP substrate [10] and GaPbuffer layer [12] may be n-type and the cap/contact layer [16] may bep-type.”

SUMMARY

It is an object of the invention to provide an efficient light emittingdevice that emits light with a peak wavelength between green and red.

Embodiments of the invention include an n-type region, a p-type region,and a light emitting layer disposed between the n-type region and thep-type region. The light emitting layer is a III-V material comprisingnitrogen and phosphorus. The device also includes a graded regiondisposed between the light emitting layer and one of the p-type regionand the n-type region. The composition in the graded region is graded.

A method according to embodiments of the invention includes growing alight emitting layer disposed between an n-type region and a p-typeregion and growing a graded region disposed between the light emittinglayer and one of the p-type region and the n-type region. The lightemitting layer is a III-V material including nitrogen and phosphorus. Acomposition in the graded region is graded or varied. As used herein,composition refers to the chemical composition of a layer, e.g. therelative amounts of constituent atoms that make up a semiconductorlayer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an LED structure formed on a GaP substrate.

FIG. 2 illustrates an LED structure grown on a GaP substrate includingat least one dilute nitride light emitting layer.

FIGS. 3 and 4 illustrate two examples of the arrangement of metalcontacts on an LED structure with at least one dilute nitride lightemitting layer.

FIG. 5 illustrates a flip chip LED structure.

FIG. 6 illustrates an LED structure from which the growth substrate hasbeen removed.

FIG. 7 is a plot of wavelength as a function of nitrogen composition fordilute nitride light emitting layers.

FIG. 8 is an energy band diagram as a function of position for an LEDstructure with thin light emitting layers.

FIG. 9 is an energy band diagram as a function of position for an LEDstructure with thick light emitting layers.

FIG. 10 illustrates a portion of a device including multiple portions ofconstant composition and/or graded composition.

DETAILED DESCRIPTION

III-phosphide and III-nitride materials are often used to make LEDs thatemit red or blue light. These materials cannot efficiently emit lighthaving peak wavelengths in the range between 500 and 600 nm, due to, forexample, poor material quality. InGaN and AlInGaP light emitting layersthat emit light having a peak wavelength between 500 and 600 nm areoften grown with fairly high levels of strain, resulting in defects thatcontribute to non-radiative recombination, which may reduce theefficiency of the LED.

In embodiments of the invention, dilute nitride InGaPN light emittinglayers grown over GaP substrates may be grown nearly lattice matched(i.e. with little or no strain) and may emit light at the desiredwavelengths. “Dilute nitride” semiconductors refer to III-V layers withnitrogen and at least one other group V atom. Examples include InGaAsNand InGaPN. The nitrogen content relative to the total group V contentis generally no more than a few %. In dilute nitride layers, the bandgap may change dramatically with a small change in nitrogen content, aproperty desirable to tune the target wavelength emission of thesesemiconductors. In GaPN alloys, the formation of subbands in the bandstructure transforms GaP, an indirect material, into a direct materialsuitable for light emitting devices such as LEDs. GaPN is in tensionwhen grown on GaP and InGaP is in compression when grown on GaP.Accordingly, an InGaPN alloy may be grown lattice-matched or nearlylattice matched to a GaP substrate.

FIG. 2 illustrates a device including a dilute nitride light emittinglayer, according to some embodiments. A light emitting or active region24, described below, is disposed between a p-type region 200 and ann-type region 32. P-type region 200 is often GaP and may be doped withany suitable p-type dopant such as Zn. N-type region 32 is often GaP andmay be doped with any suitable n-type dopant such as Si. N-type region32 and p-type region 200 are often GaP because GaP is typicallytransparent to light emitted by the active region 24, which may have apeak wavelength that is red, red-orange, amber, yellow, or green. N-typeregion 32 and p-type region 200 may be any other suitable material, suchas ternary materials including but not limited to InGaP and GaPN, andquaternary materials. N-type region 32 and p-type region 200 need nothave the same composition, though they may.

In some embodiments, substrate 20, described below, is p-type GaP andp-type GaP region 200 may be omitted.

Substrate 20 is often GaP, which has a band gap of ˜2.26 eV or ˜549 nm,and is thus transparent to light at likely peak wavelengths emitted bythe active region 24, i.e. red, red-orange, amber, yellow, or greenlight. A GaP substrate may be doped p-type with Zn or any other suitabledopant or doped n-type with Si or any other suitable dopant. Othersubstrates with an a-lattice constant close to the a-lattice constant ofGaP may be used, or with an a-lattice constant that is close to thea-lattice constant of the InGaPN light emitting layers or other layersin the device. Examples of suitable substrates include Si, AlInP, ZnS,Ge, GaAs, and InP. Silicon which is inexpensive but absorbing of lightat likely peak wavelengths emitted by the active region 24 may be usedbut is often removed. The growth substrate may be removed after growthof the above-described semiconductor structure, may be thinned aftergrowth of the above-described semiconductor structure, or may remainpart of the finished device. Absorbing substrates such as Si are oftenremoved. In some embodiments, a semiconductor device structure 21 isgrown on substrate 20 by any suitable epitaxial technique, such asmetal-organic chemical vapor deposition, vapor-phase epitaxy, ormolecular beam epitaxy. As used herein, “semiconductor device structure”may refer to semiconductor layers that are grown on the substrate, suchas n-type layers, p-type layers, or layers in the active region.

In the device illustrated in FIG. 2, the substrate 20 may be p-type,thus any p-type layers are grown first, followed by active region 24,followed by any n-type layers, such as n-type region 32. In someembodiments, the substrate is n-type, such as n-GaP. On an n-typesubstrate, the semiconductor structure 21 illustrated in FIG. 2 may begrown in reverse, such that the n-type layers including n-type region 32are grown first, followed by the active region 24, followed by thep-type layers including p-type region 200. Either structure, i.e. astructure with the p-type layers grown first or a structure with then-type layers grown first, may be grown on an undoped substrate, such asSi.

In some embodiments, a graded region 22 is grown between p-type region200 and active region 24, as illustrated in FIG. 2. In some embodiments,the composition of graded region 22 is graded. In some embodiments, thedopant concentration in graded region 22 is graded in addition to orinstead of composition. Graded region 22 may be p-type or undoped. Ap-type graded region 22 may be no more than 500 nm thick in someembodiments. An undoped graded region 22 may be no more than 100 nmthick in some embodiments.

As used herein, the term “graded” when describing the composition in alayer or layers in a device is meant to encompass any structure thatachieves a change in composition in any manner other than a single stepin composition. Each graded layer may be a stack of sublayers, each ofthe sublayers having a different composition than either sublayeradjacent to it. If the sublayers are of resolvable thickness, the gradedlayer is a step-graded layer. In some embodiments, the sublayers in astep-graded layer may have a thickness ranging from several tens ofangstroms to several thousands of angstroms. In the limit where thethickness of individual sublayers approaches zero, the graded layer is acontinuously-graded region. The sublayers making up each graded layercan be arranged to form a variety of profiles in composition versusthickness, including, but not limited to, linear grades, parabolicgrades, and power-law grades. Also, graded layers or graded regions arenot limited to a single grading profile, but may include portions withdifferent grading profiles and one or more portions with substantiallyconstant composition.

The composition in a semiconductor layer may be graded by varying one ormore of the growth temperature, the flow rates of precursor materialsduring growth, and the relative flow rates of different precursormaterials during growth.

The composition of graded region 22 may be graded from AlGaP or GaP in aportion of region 22 adjacent to p-type region 200 to AlGaP or AlP in aportion of region 22 adjacent to active region 24. For example, thecomposition of aluminum in an AlxGa1-xP graded region 22 in a portionclosest to p-type region 200 may be x=0 in some embodiments, x≤0.05 insome embodiments, and x≤0.1 in some embodiments. The composition may begraded to an aluminum composition in a portion of AlxGa1-xP gradedregion 22 closest to active region 24 of x=1 in some embodiments, x≥0.95in some embodiments, and x≥0.9 in some embodiments.

In some embodiments, graded region 22 is omitted and active region 24 isdisposed in direct contact with p-type region 200.

A light emitting or active region 24 is grown on graded region 22 or onp-type region 200. In some embodiments, active region 24 includes asingle thick or thin light emitting layer. In some embodiments, activeregion 24 includes multiple light emitting layers 26 separated by one ormore barrier layers 28, as illustrated in FIG. 2. Light emitting layers26 may be quantum wells in some embodiments. Though three light emittinglayers 26 and two barrier layers 28 are illustrated in FIG. 2, activeregion 24 may include more or fewer light emitting layers and barrierlayers. Barrier layers 28 separate light emitting layers 26. Barrierlayers 28 may be, for example, GaP, AlGaP, AlInGaP, InGaPN, or any othersuitable material with a larger band gap than light emitting layers 26.

The composition of light emitting layers 26 may be selected such thatthe light emitting layers emit light have a peak wavelength in a rangefrom green to yellow to red. In some embodiments, light emitting layers26 are InxGa1-xP1-yNy. The subscript x refers to the In content and thesubscript y refers to the N content. The composition x may be at least0.01 in some embodiments and no more than 0.07 in some embodiments. Thecomposition y may be at least 0.005 in some embodiments and no more than0.035 in some embodiments. In order for an InGaPN light emitting layerto be lattice matched when grown on GaP, x=(2 to 2.4)y. In someembodiments, x is at least twice y. In some embodiments, x is no morethan y multiplied by 2.5. In some embodiments, x is y multiplied by 2.4.In a device with AlGaP barriers and light emitting layers thicker than10 nm, the light emitting layers may emit light having a green peakwavelength when y=0.005 (0.5%) and x=0.01, a yellow peak wavelength wheny=0.015 (1.5%) and x=0.03, and a red peak wavelength when y=0.035 (3.5%)and x=0.07. FIG. 7 illustrates estimated wavelength as a function of Ncontent (y) for several compositions of N in a device with AlGaPbarriers and InxGa1-xP1-yNy light emitting layers thicker than 10 nm,where x=2y. If the barriers are GaP, the compositions illustrated inFIG. 7 will result in approximately the same peak wavelengths asillustrated in FIG. 7. If the barriers are AlP, the curve illustrated inFIG. 7 may shift by at most 50 nm toward blue, meaning that lightemitting layers that emit a peak wavelength that is blue (i.e. at about510 nm) may be fabricated.

In some embodiments, InGaPN light emitting layers 26 are lattice matchedto a GaP substrate 20, such that light emitting layers 26 areunstrained. In some embodiments, InGaPN light emitting layers 26 are acomposition that is strained when grown on substrate 20. The compositionof the light emitting layers may be selected such that the latticeconstant of a theoretical relaxed material of the same composition asthe light emitting layer differs from the lattice constant of substrateby less than 1% in some embodiments and less than 0.5% in someembodiments.

Light emitting layers 26 may be at least 2 nm thick in some embodiments,no more than 10 nm thick in some embodiments, at least 10 nm thick insome embodiments, and no more than 100 nm thick in some embodiments.Barrier layers 28 may be no more than 200 nm thick in some embodiments,no more than 100 nm thick in some embodiments, and at least 20 nm thickin some embodiments. For example, in an active region with thick lightemitting layers (i.e. between 10 nm and 100 nm thick), the barrierlayers may be less than 100 nm thick. In an active region with thinlight emitting layers (i.e. between 3 nm and 10 nm thick), the barrierlayers may be between 20 nm and 100 nm thick.

In some embodiments, a second graded region 30 is grown over activeregion 24, in direct contact with n-type region 32. The composition ofgraded region 30 may be graded from AlGaP in a portion of region 30adjacent to active region 24 to GaP in a portion of region 30 adjacentto n-type region 32. For example, the composition in the portion ofAlxGa1-xP graded region 30 closest to active region 24 may be x=1 insome embodiments, x≥0.8 in some embodiments, and x≥0.9 in someembodiments. The composition in the portion of AlxGa1-xP graded region30 in a portion closest to n-type region 32 may be x=0 in someembodiments, x≤0.05 in some embodiments, and x≤0.1 in some embodiments.Graded region 30 may be undoped or doped with an n-type dopant such asSi. An n-type graded region 30 may be no more than 500 nm thick in someembodiments. An undoped graded region 30 may be no more than 100 nmthick in some embodiments.

In some embodiments, graded region 30 is omitted and n-type region 32 isdisposed in direct contact with active region 24.

The use of one or both of p-type graded region 22 and n-type gradedregion 30 may minimize band discontinuities in the device, which mayreduce the series resistance and the forward voltage of the device. Inaddition, graded regions 22 and/or 30 may reduce or eliminatewaveguiding at the intersection of two materials with different indicesof refraction, which may increase the amount of light extracted from thedevice.

FIG. 8 illustrates band energy as a function of position for a firstexample of a structure illustrated in FIG. 2. P-type region 200 andn-type region 32 have the largest band gaps in the structure. Lightemitting layers 26 have the smallest band gaps in the structure. Inactive region 24, light emitting layers 26 are separated by barrierlayer 28, which have a larger band gap than the light emitting layers26. The valence band 50 and the conduction band 52 are flat (i.e.horizontal) in the areas corresponding to p-type region 200, lightemitting layers 26, barrier layers 28, and n-type region 32, indicatingthat these areas have a constant band gap resulting from a constantcomposition. Though FIG. 8 illustrates the n-type region 32, the barrierlayers 28, and the p-type region 200 as having the same band gap, insome embodiments they need not have the same band gap. The verticalparts of the valence band 50 and conduction band 52 indicate stepchanges in composition. Graded region 22 includes a region 104 ofconstant composition, which may be AlP. Between constant compositionregion 104 and p-type region 200 is a graded region 108. Graded region30 includes a region 102 of constant composition, which may be AlP.Between constant composition region 102 and n-type region 32 is a gradedregion 106. In the graded regions 106 and 108, the valence band 50 issloped, indicating that the band gap and therefore the composition aremonotonically, linearly graded. The conduction band 52 is not slopedbecause in AlGaP layers, only the valence band may be affected by the Alcontent. In the device illustrated in FIG. 8, the p-type region 200 andn-type region 32 are GaP. The graded regions 106 and 108 are AlxGa1-xP,where x is graded from 0 in a portion of the graded region closest toGaP layer 32 or 200 to 1 in a portion of the graded region closest toconstant composition regions 102 and 104. The regions 102 and 104 ofconstant composition may be, for example, at least twice the thicknessof one of the barrier layers in the device. The light emitting layers 26are InGaPN, with one or more compositions as described above inreference to FIG. 7, and the barrier layers are AlP. The light emittinglayers are between 2 nm thick and 10 nm thick in some embodiments.

FIG. 9 illustrates band energy as a function of position for a secondexample of a structure illustrated in FIG. 2. P-type region 200 andn-type region 32 have the largest band gaps in the structure. Lightemitting layers 26 have the smallest band gaps in the structure. Inactive region 24, light emitting layers 26 are separated by barrierlayer 28, which have a larger band gap than the light emitting layers26. The valence band 50 and the conduction band 52 are flat (i.e.horizontal) in the areas corresponding to p-type region 200, lightemitting layers 26, barrier layers 28, and n-type region 32, indicatingthat these areas have a constant band gap resulting from a constantcomposition. The vertical parts of the valence band 50 and conductionband 52 indicate step changes in composition. Graded region 30 isomitted. Graded region 22 includes a first portion 70 of constantcomposition (i.e. flat valence and conduction bands) and a secondportion 72 where the composition is graded (i.e. sloped valence band50), indicating that the band gap and therefore the composition inportion 72 are monotonically, linearly graded. In the graded portion 72,the material may be AlxGa1-xP, where x is graded from between 0.5 and 1adjacent to GaP portion 70 to between 0.2 and 0 in a portion of thegraded region closest to p-type region 200. A step change 74 indicatesthe transition between GaP in portion 70 and AlP at the left-most edgeof graded portion 72. In the device illustrated in FIG. 9, the p-typeregion 200 and n-type region 32 are GaP. Constant composition portion 70may be, for example, at least as thick as one of the barrier layers inthe device. The light emitting layers 26 are InGaPN, with one or morecompositions as described above in reference to FIG. 7, and the barrierlayers are GaP. The light emitting layers are between 10 nm thick and100 nm thick in some embodiments.

Any graded regions in the device may include multiple portions ofconstant composition and/or graded composition. A graded region withmultiple portions of graded composition may have the same or differentgrading profiles in the portions of graded composition. For example, agraded region can include a portion of constant composition GaP adjacentto the light emitting region, followed by a portion of AlGaP that isgraded from 0% Al to 100% Al, followed by a portion of constantcomposition AlP having a thickness of less than 110 nm, followed by aportion of AlGaP graded from 100% Al to 0% Al adjacent to the n-type orp-type GaP layer 32 or 200, depending on the location of the gradedregion in the device. In another example, a graded region includes aportion of constant composition GaP adjacent to the light emittingregion, followed by a graded portion of AlGaP that is graded from 0% Al(GaP) to between 50 and 100% Al, followed by a portion of constantcomposition AlGaP that is between 50% and 100% Al, followed by gradedportion of AlGaP that is graded from the Al composition in the constantcomposition portion to 0% (GaP) adjacent to the n-type or p-type GaPlayer 32 or 200, depending on the location of the graded region in thedevice.

FIGS. 3, 4, 5, and 6 illustrate finished LEDs, including any of thesemiconductor structures described above and metal contacts formed onthe n-type region 32 and the p-type substrate 20 or p-type region 200.The metal contacts are used to forward bias the device. In the devicesillustrated in FIGS. 3 and 4, the growth substrate 20 remains part ofthe device. In the devices illustrated in FIGS. 5 and 6, the growthsubstrate is removed from the semiconductor structure.

In the structures illustrated in FIGS. 3 and 4, an n-contact 34 isformed on a portion of the n-type region 32. N-contact 34 may be, forexample, any suitable metal including Ge, Au, and Ni. In someembodiments, n-contact 34 is a multi-layer contact. For example,n-contact 34 may include a Ge layer in direct contact with n-type region32, followed by Au, Ni, and Au layers.

In the structure illustrated in FIG. 3, conductive dots 36 makeelectrical contact to p-type GaP substrate 20. Dots 36 may be, forexample, AuZn. Dots 36 may be embedded in a mirror 38. Mirror 38 may beany suitable reflective material including, for example, a layer of SiO2in direct contact with substrate 20, and a layer of Ag formed over theSiO2. A second mirror 40 is formed such that conductive dots 36 arepositioned between mirror 40 and substrate 20. Mirror 40 may be aconductive material such as a metal, Ag, Al, or any other suitablematerial. In the structure illustrated in FIG. 3, the p-type substrate20 is thick enough to efficiently spread the current laterally over asignificant distance on the p-side of active region 24. P-doped GaPsubstrates (doped with Zn) are available in thicknesses of about 200 to400 μm. Current can spread about 0.2 mm in a p-GaP substrate 300 μmthick. In some embodiments, conductive dots 36 are placed no furtherapart than the current spreading distance of the substrate 20.Conductive dots 36 may be at least 10 μm wide in some embodiments and nomore than 100 μm wide in some embodiments. Conductive dots 36 may bespaced at least 100 μm apart in some embodiments, at least 200 μm apartin some embodiments, and no more than 500 μm apart in some embodiments.

In the structure illustrated in FIG. 4, a full sheet contact 42 which isreflective is formed in direct contact with p-type GaP substrate 20.Sheet contact 42 may be, for example, AuZn or any other highlyreflective layer that forms an ohmic contact with GaP.

FIGS. 5 and 6 illustrate devices where the growth substrate 20 isremoved.

FIG. 5 is a flip chip device. An n-contact 34 is formed on n-type region32, then a portion of the n-contact 34, n-type region 32, graded region30, and active region 24 are etched away to form a mesa exposing aportion of graded region 22, which may be p-type, or p-type region 200,on which a p-type contact 42 is formed. A gap 43, which may be filledwith a solid material such as a dielectric, electrically isolates n- andp-contacts 34 and 42. The device may be attached to a mount (not shown)to support the semiconductor structure 21, or n- and p-contacts may beformed to support the semiconductor structure 21. The growth substrateis then removed, revealing a surface of p-type region 200. The growthsubstrate may be removed by any suitable technique, including wet or dryetching, mechanical techniques such as grinding, or laser melting. N-and p-contacts 34 and 42 may be reflective, and the device mounted suchthat a majority of light is extracted through the top surface of p-typeregion 200, in the orientation illustrated in FIG. 5.

In FIG. 6, the semiconductor structure is bonded to a host substrate 60through the top surface of n-type region 32 of semiconductor structure21. One or more optional bonding layers, not shown in FIG. 6, may bedisposed between host substrate 60 and semiconductor structure 21. Hostsubstrate 60 mechanically supports the semiconductor structure 21 duringremoval of the growth substrate 20, not shown in FIG. 6. Removing thegrowth substrate exposes a bottom surface of p-type region 200, on whicha p-contact 62 is formed. P-contact 62 may be any suitable contact,including the contacts described above in reference to FIGS. 3 and 4. Ann-contact 34 is formed on host substrate 60. In the device illustratedin FIG. 6, host substrate 60 must be conductive. Examples of suitablehost substrate materials include n-type GaP. Host substrate 60 may betransparent and n-contact 34 limited in extent so a majority of light isextracted through the top surface of host substrate 60. Alternatively,host substrate 60 may be reflective and the p-contact 62 may betransparent or limited in extent so a majority of light is extractedthrough p-contact 62 and/or p-type region 200.

In some embodiments, host substrate 60 is not conductive and the n- andp-contacts are formed in a flip chip formation, as illustrated in FIG.5. Examples of suitable host substrate materials include sapphire andglass.

Having described the invention in detail, those skilled in the art willappreciate that, given the present disclosure, modifications may be madeto the invention without departing from the spirit of the inventiveconcept described herein. Therefore, it is not intended that the scopeof the invention be limited to the specific embodiments illustrated anddescribed.

The invention claimed is:
 1. A device comprising: a substrate; a p-typeregion disposed on the substrate; an n-type region; a III-V materiallight emitting layer, that comprises nitrogen and phosphorus, disposedbetween the n-type region and the p-type region; a graded regiondisposed between the light emitting layer and the n-type region, thegraded region including a composition that is graded; a first contactcomprising a mirror and conductive dots embedded in the mirror, thefirst contact disposed on the substrate; and a second contact disposedon the n-type region.
 2. The device of claim 1 including the lightemitting layer being InGaN_(x)P_(1−x), where 0<X≤0.03.
 3. The device ofclaim 1 including the light emitting layer has a composition that whenforward biased emits light having a peak wavelength in a range of greento red.
 4. The device of claim 1 including the graded region being afirst graded region, the device further comprising a second gradedregion disposed between the light emitting layer and the p-type region,the second graded region including a composition that is graded.
 5. Thedevice of claim 1 including the composition in the graded region beinggraded from a composition of GaP in a portion of the graded regionclosest to the n-type region to a composition of AlGaP in a portion ofthe graded region closest to the light emitting layer.
 6. The device ofclaim 1 including the n-type region and the p-type region being GaP. 7.The device of claim 1 including the substrate being p-type GaP.
 8. Thedevice of claim 1 including the first contact that comprises areflective metal.
 9. The device of claim 8 including the reflectivemetal being a full sheet of AuZn.
 10. The device of claim 1 including:the mirror that comprises a layer of SiO₂ in direct contact with thesubstrate and a layer of Ag disposed on the layer of SiO₂; and theconductive dots being AuZn.
 11. The device of claim 1 further comprisinga second mirror, the conductive dots being disposed between the secondmirror and the substrate.
 12. The device of claim 11 including thesecond mirror that is one of metal, Ag, and Al.
 13. A device comprising:a p-type region; an n-type region; a III-V material light emittinglayer, that comprises nitrogen and phosphorus, disposed between then-type region and the p-type region; a p-type graded region disposedbetween the light emitting layer and the p-type region, including acomposition in the graded region that is graded; a first contactdisposed in electrical contact with the p-type region and the firstcontact disposed in contact with the p-type graded region; and a secondcontact disposed on the n-type region, the first and second contacts areformed on a same side of the device.
 14. The device of claim 13 furthercomprising an etched mesa that exposes a surface of a p-type layer onwhich the first contact is formed.
 15. The device of claim 13 includingthe light emitting layer being InGaN_(x)P_(1−x), where 0<X≤0.03.
 16. Thedevice of claim 13 including the light emitting layer that has acomposition that when forward biased emits light having a peakwavelength in a range of green to red.
 17. A device comprising: asubstrate; a p-type region disposed on the substrate; an n-type region;a III-V material light emitting layer, that comprises nitrogen andphosphorus, disposed between the n-type region and the p-type region; agraded region disposed between the light emitting layer and the n-typeregion, the graded region including a composition that is graded; afirst contact comprising a reflective metal, the first contact disposedon the substrate; and a second contact disposed on the n-type region.